The vast majority of antibodies produced during HIV infection or as a consequence of vaccination fail to neutralize primary isolate virus. This is not surprising given (1) the structure of the HIV-1 envelope glycoprotein - most of the neutralizing epitopes are obscured or only transiently exposed; and (2) the fact that the immune system cannot differentiate between merely immunogenic and critically protective epitopes. The majority of highly effective neutralizing human monoclonal antibodies for specific epitopes have relatively unique or unusual structural features. It has also been shown that passive administration of some anti- IV neutralizing antibodies, usually in combination, can prevent infection or transmission in nonhuman primate models and have a prolonged impact on viral load when used in combination with anti-retroviral therapy in non-human primates. One of the more immunogenic regions of the HIV-1 envelope glycoprotein is the immunodominant, ectodomain of gp41. Antibodies to this region are prevalent in HIV-1 infected individuals; however, monoclonal antibodies to the immunodominant (ID) ectodomain are not associated with HIV-1 neutralization. We have now shown that post-translational modification in the glycosylation of one non-neutralizing anti-gp41 ID antibody, F240, conferred robust neutralizing activity on the antibody. We believe this may be a more generalized mechanism of activation for antibodies to this epitope and that understanding the contribution of the specific post-translational modifications of this class of antibodies will make it possible to identify mechanisms to direct the post-translational modification of antibodies in B cells of immunized individuals. To explore this hypothesis, we propose to identify other human monoclonal antibodies to gp41 ID epitope which neutralize when glycosylated in CHO cells. We hypothesize that, similar to that observed for F240, differential glycosylation of other human monoclonal antibodies (HMAb) to the gp41 ID epitope, but not necessarily all, will result in HIV neutralization. Furthermore, serum antibodies to the immunodominant domain will be characterized as to glycosylation patterns and differentially glycosylated antibodies purified to test for neutralization. We hypothesize that differential glycosylation will be observed for serum antibodies with a low prevalence of glycosylation similar to that seen for CHO expressed F240 antibody and which may be used to predict effective serum based antibody mediated protection. [unreadable] [unreadable] [unreadable]